while True:
    username = input("请输入用户名：")
    # 判断是否exit
    if username == "exit":
        break
    password = input("请输入密码：")
    # 判断账号密码
    if username == "root" and password == "1111":
        print("登录成功！")
        # 结束程序
        break
    else:
        print("用户名或密码错误！")
    pass